An electromechanical power transmission chain of a mobile working machine comprises typically one or more electrical machines and one or more electronic power converters. The electromechanical power transmission chain can be a series transmission chain where one of the electrical machines operates as a generator and the one or more electronic power converters are arranged to convert the electrical voltages produced by the generator into electrical voltages having amplitudes and frequencies suitable for the one or more other electrical machines. The generator can be driven with a combustion engine that can be e.g. a diesel engine, an Otto-cycle engine, or a turbine engine. The other electrical machines can be, for example, electrical motors arranged to drive wheels, chain tracks, or other actuators of the mobile working machine. It is also possible that the electromechanical power transmission chain is a parallel transmission chain where an electrical machine that is mechanically connected to a combustion engine operates sometimes as a generator which charges one or more energy-storages and sometimes as a motor that receives electrical energy from the one or more energy-storages and assists the combustion engine when high mechanical output power is needed. It is also possible that the electromechanical power transmission chain is between a battery element and one or more actuators of the mobile working machine. In this case, the electromechanical power transmission chain may comprise an electrical motor for driving the one or more actuators and an electronic power converter between the battery element and the electrical motor. The mobile working machine can be, for example, a tractor, a bucket charger, a road drag, an excavator, or a bulldozer.
The electromechanical power transmission chain provides advantages compared to a traditional mechanical power transmission chain because, for example, the rotational speed of the combustion engine can be more freely selected from the viewpoint of the operational efficiency of the combustion engine, and thus savings in the fuel costs can be achieved. However, there is still a need to reduce operating costs of working machines of the kind mentioned above.
The publication US2010097037 describes a method for controlling an electromechanical power transmission chain of a mobile working machine so that capacitance of a capacitive energy storage circuit can be minimized and also the peak power taken from a combustion engine of the mobile working machine can be reduced. This control method is, however, based on an assumption that the temporal variation of the load is predictable. This assumption, however, is not valid in a general case.